The present invention relates to a system for feedback control of the air-fuel ratio in response to a signal from an oxygen sensor, or more in particular to a system for suspending the feedback control at the time of the heavy load of the engine.
Conventional vehicle engines comprise an oxygen sensor in the exhaust system for detecting the air-fuel ratio from the oxygen concentration so that the air-fuel ratio is subjected to feedback control by the detection signal of the oxygen sensor. The disadvantage of this system is that the feedback control under heavy engine load results in an excessively lean mixture, thus deteriorating the operating performance. If the feedback control is suspended immediately after reaching the heavy load condition, the operating performance would be improved. The problem, however, is that the enriched mixture increases the amount of HC and CO exhausts.